SU1739182A1 - Differential capacity transducer for linear displacements - Google Patents

Description

Differential linear capacitive displacement sensor contains two electrodes installed with a gap, two communication capacitors connected between them and the sensor output terminals and a screen placed in the gap between the electrodes, connected to the common ground point and mounted for normalization to the electrodes.

The electrical capacitance of the coupling capacitors is several times smaller than the capacitance of one of the electrodes relative to the screen, with the screen being symmetrically positioned between the electrodes.

The drawing shows a diagram of a differential capacitive linear displacement sensor.

The sensor contains two electrodes 1 installed with a gap and two coupling capacitors 2 connected between electrodes 1 and the output terminals 3 of the sensor. A shield 4 is placed in the gap between the electrodes 1, connected to the common ground point 5 and mounted for movement along the normal to the electrodes 1. In the measurement process, the screen 4 is connected with the test object (not shown).

Differential capacitive linear displacement sensor works as follows.

If the capacitances of the capacitors 2 are equal to each other, then in the initial state of the sensor, when the screen 4 is symmetrically located in the gap between the electrodes 1; the capacitances Ci and C2 of the output terminals 3 of the sensor relative to the screen 4 are also equal to each other, which corresponds to the zero value of the differential capacitance DC1 MF - € 2. When screen 4 is moved from the position of symmetry by the value of x, the capacitances Ci (x) and Ca (x) change in such a way that one of them increases with x, and the other decreases. The dependence DC1 (x), representing the output characteristic of the sensor, is described by

, I 2 Ј0 S x

DS1

d2 (1 n-K) 2 - Ј) 2

0)

where Oo is dielectric constant;

5 10

15 20 25

thirty

35 40 45

S is the area of the electrode 1;

d is the distance between the electrodes 1 and the screen 4 in the symmetry position of the screen 4;

K Ј0 S / (Cd) is a coefficient that shows how many times the capacitance C of the capacitors 2 of the coupling is less than the capacitance Ј0 S / d of one of the electrodes 1 relative to the screen 4 with its symmetrical arrangement between the electrodes 1.

It can be seen from formula (1) that in the case of K O (the plates of capacitors 2, the connections are short-circuited) with large displacements of the screen 4, when Ixl, | DC | - ° about. This indicates the nonlinearity of the output characteristic of the sensor at the edges of the measurement range, if the conditions for its linearization are not met,

If the capacitance C of capacitors 2 is several times smaller than the capacitance of one of the electrodes 1 relative to the screen 4 in the position of its symmetry between electrodes 1 and the coefficient K satisfies the inequality (1 + K) 2 1, then the subtracted denominator of the formula (1) can be neglected and write ds „2ЈoS

d2 (1 + K) 2

Expression (2) represents the linearized output characteristic of the sensor at the edges of the measuring range, where | x I d.

Claims (1)

Invention Differential Capacitive Linear Motion Sensor, containing two gap-mounted electrodes, two coupling capacitors connected between them and the output terminals of the sensor, and a screen located in the gap between the electrodes and connected to the normal to the electrodes, which is different in order to linearize the output characteristic at the edges of the measuring range, the electrical capacitance of the coupling capacitors is less than the capacitance of one of the electrodes from screen with a symmetrical arrangement of the screen between the electrodes.